A similar process is described in U.S. Pat. No. 5,264,616. U.S. Pat. No. 5,264,616 discloses a process for the preparation of an alkyl 5-formylvalerate starting from alkyl 4-pentenoate, alkyl 3-pentenoate or mixtures of alkyl 2-, 3- and 4-pentenoate in the presence of a catalyst system comprising rhodium (Rh) and a bidentate phosphite ligand.
A disadvantage of this process is that the activity of the catalyst system is low. Moreover the activity of the catalyst system decreases when the catalyst system is reused several times. The lower activity and stability of the catalyst system is especially found when the mixture of pentenoate esters contains (even small amounts of) cis 2-pentenoate ester.